Spike problem CMS Electromagnetic Calorimeter ECAL Measures energies

Spike problem

CMS Electromagnetic Calorimeter (ECAL) • Measures energies of electrons and photons. • Ideal for stopping high energy particles. • Made from crystals of lead tungstate (Pb. WO 4). • Backed by silicon APD’s o APD - Avalanche Photo Diode , VPT vaccum phototriodes. o Converts light to electricity. • Number of crystals in ECAL 75848 crystals organized into barrel and endcaps.

CMS Trigger system • The Level 1 (L 1) trigger is a hardware trigger close to the detector, consisting of super fast electronics. • The High Level Trigger (HLT) is a software trigger. • The trigger system reduces the number of events from about 40 million per second (40 MHz) to ~ 100 per second. • RAW data from CMS would be ~ 40 terabytes per second. • After the trigger roughly 100 MB per second remain.

Spike phenomenology • Isolated high energy deposits in ECAL Barrel (EB) o Occur at a rate proportional to the intensity of the proton beams. o Produced by direct ionization of the APD’s by particles created in pp collisions. o Presents issues for triggering CMS at high luminosity. - On average, one spike with transevrse energy > 3 Ge. V is observed per 370 minimum-bias triggers in CMS

CMS Event Display of a pp collision event, showing an isolated ECAL spike corresponding to a 690 Ge. V transverse energy deposit.

Now we want to see the spikes in the data

Rechit energy

Swiss Cross Variable Swiss-cross variable defined as: 1 -E 4/E 1

Swiss Cross on 2012 D data Number of events Swiss cross variable

2013 MC data Number of events Swiss cross variable

Spike can be solved : 1. Online rejection. 2. Offline rejection.

Online rejection:

Offline rejection: • Cut on topology (”Swiss-cross” variable). • Cut on timing.

Problems and motivation: Problems: 1. Accessing the online system. 2. Accessing Oracle database that contains the nonevent data. Motivation: Apply and tuning s. FGVB thresholds on the channels and compile it with the emulator on CMSSW. .

Thanks • • Alex Zaby. Nadir. Philippe Minne Sherif Elgammal